Best way to sort a DropDownList in MVC3 / Razor using helper method

本文转自：http://stackoverflow.com/questions/7223185/best-way-to-sort-a-dropdownlist-in-mvc3-razor-using-helper-method

The first and most important part of your code would be to get rid of any ViewBag/ViewData (which I personally consider as cancer for MVC applications) and use view models and strongly typed views. 

So let's start by defining a view model which would represent the data our view will be working with (a dropdownlistg in this example):
public class MyViewModel
{
    public string SelectedItem { get; set; }
    public IEnumerable<SelectListItem> Items { get; set; }
}
then we could have a controller:
public class HomeController : Controller
{
    public ActionResult Index()
    {
        var model = new MyViewModel
        {
            // I am explicitly putting some items out of order
            Items = new[]
            {
                new SelectListItem { Value = "5", Text = "Item 5" },
                new SelectListItem { Value = "1", Text = "Item 1" },
                new SelectListItem { Value = "3", Text = "Item 3" },
                new SelectListItem { Value = "4", Text = "Item 4" },
            }
        };
        return View(model);
    }
}
and a view:
@model MyViewModel
@Html.DropDownListForSorted(
    x => x.SelectedItem, 
    Model.Items, 
    new { @class = "foo" }
)
and finally the last piece is the helper method which will sort the dropdown by value (you could adapt it to sort by text):
public static class HtmlExtensions
{
    public static IHtmlString DropDownListForSorted<TModel, TProperty>(
        this HtmlHelper<TModel> helper, 
        Expression<Func<TModel, TProperty>> expression, 
        IEnumerable<SelectListItem> items, 
        object htmlAttributes
    )
    {
        var model = helper.ViewData.Model;
        var orderedItems = items.OrderBy(x => x.Value);
        return helper.DropDownListFor(
            expression, 
            new SelectList(orderedItems, "Value", "Text"), 
            htmlAttributes
        );
    }
}